High-frequency multiplex-signaling system



Sept 22,1925.

H. A. AFFEL HIGH FREQUENCY MULTIPLEX SIGNALING SYSTEM Filed Sept. 30. 1919 Law Pass Filter 5 High Frequ ency Band F/lier L T Hi I! Fre uenc 1 1 9 Q52 5 T Law Freyuellcy A 1 Transformer Law/ ass FfHer' fre uemcnrrl'er Cur-ieni Line Baiancin fieiwork 9 MD1 High Freguenrg BandF/Her IN VEN TOR.

. A TORNEY Patented Sept. 22, 1925.

UNITED STATES PATENT OFFICE.

HERMAN A. AFFEL, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

HIGH-FREQUENCY MULTIPLEX-S IGNALING SYSTEM.

Application filed September 30, 1919. Serial No. 327,455.

To all whom it may concern:

Be it known that I, HERMAN A. AFFEL, res

siding at Brooklyn, in the county of Kings and State of New York, have invented certain Improvement in High-Frequency Multiplex-Signaling Systems, of which the following is a specification.

This invention relates to high frequency multiplex signaling systems, and more particularly to a terminal circuit arrangement embodying the use of a common translating circuit adapted both to modulate the transmitted current and to demodulate the high frequency received current.

In the multiplex signaling systems heretofore used which employ a' plurality of of carrier frequencies for transmission of a plurality of low frequency signaling'currents, it has been customary to insert in the transmitting and receiving paths of the terminal circuits of such system a translating circuit individual to each of said paths. It is the object of this invention to provide means whereby the low frequency signaling current and the high frequency received oscillations may be impressed upon a common translating circuit wherein the carrier oscillations will be modulated by the low frequency variations and also the high frequency received oscillations will be demodulated by the said carrier oscillations, the said translating circuit being so de: signed as to prevent the transmission of oscillations of the carrier frequency.

This invention will be better understood from the following description when read in connection with the attached drawing of which Figure 1 shows a terminal clrcuit employing a balanced duplex translatlng device, and Figure 2 shows a similar type of circuit in which the translating operations are performed by a single translating device.

In Figure 1 L, represents a line having low frequency signaling apparatus connected thereto by means of which low frequency signaling currents may be impressed upon the terminal circuit. The line L is related to the terminal circuit by means of the triple-winding transformer T, having associated therewith network N which is adapted to balance the line L,. The low frequency branch 1 of the four-wire circuit has the low pass filter F inserted therein which is adapted to pass low frequency 'taining the translating device MD current to the translating circuit andto prevent high frequency oscillations -from the branch 2 from --passing through the circuit 1 into the low frequency line. The high frequency branch *3 of the transmitting path has therein a high frequency band filter F which is adapted to transmit the modulated high frequency oscillations but prevent the passage of low frequency currents, resulting from the demodulation of the high frequency oscillations. L represents a high frequency line over which the modulated high frequency oscillations are transmitted to and from the terminals at the, opposite ends of the said line. The-four-wlre ter minal circuit is related to the line L by the triple-winding transformer T which has associated with it a network N adapted to balance the line L. The high frequency branch 2 of the receiving path has therein a high frequency band filter F which is adapted to transmit the high frequency oscillations to the translating circuit and to prevent the low frequency currents from branch 1 from passing to the line L over the branch 2. The low frequency branch 4 of the receiving path has therein a low pass filter F which is adapted to'pass low. frequency signaling current and to prevent the high frequency oscillations from the translating device from passing to the line L .A transformer T Which'may be of a' type for the efiicient' transmission of both low frequency and high frequency currents, im-

presses these currents upon the circuit clalae out put side of the translating circuit is connected by the transformer T with the low frequency branch and the high frequency branch of the receiving and the transmittin paths respectively. The unmodulated hig frequency oscillations for the translating processes of the device MD are sup lied by a source G which may belany wel known type of device for generating high-frequency sinusoidal oscillations.

Having in mind the functions to be erformed by the various parts just descri ed, the invention will be clearly shown from the following description of the mode of operation ,of the circuit. Low frequency signaling currents set up in the line L by the signaling apparatus associated therewith, will be impressed b means of the transformer T upon the ow frequency branch 1 11 of the transmitting path. This current will pass through the filter F and be impressed by means of the transformer T .upon the translating circuit. The unmodulated hi h frequency oscillations from the source which are also impressed upon the translating circuit,- will be modulated by-the voice currents, and the modulated highfrequency oscillations will be impressed y means of the transformer T upon the high frequency branch 3 of the-transmitting path. These modulated oscillations will pass through the high frequency band filter F and be transmitted over the high frequency line L to a terminal circuit at the opposite end of the said line which may be of the same type as that shown in Figure 1 Modulated high frequency oscillations received over the line L will be impressed by the transformer T upon the high frequency branch 2 of the re ceiving path. These oscillations will pass through the high frequency band filter F and be impressed upon the translatin circuit by means of the transformer T These oscillations will be demodulated b the carrier oscillations from the source and the low f uency currents resulting from demodulation will pass through the low pass filter F into the branch 4 of'the receiving path and be impressed uporrthe line L actuating the low frequency signaling apparatus associated therewith.

It will be seen that this arrangement discloses a method and means Whereby 'a single translating circuit performs the modulation and the demodulation of the currents in the transmitting and receiving paths of the fourwire terminal circuit which circuit is characterized by the use of networks to balance the two-wire'line circuits, by the use of selective networks or filtersin the two-wire paths of the four-wire circuit and also by the use of a balanced translating circuit in which the radiation therefrom of oscillations of carrier frequency is prevented.

Figure 2 showsa circuit arrangement in which low frequency signaling apparatus represented by a transmitte'rT and receiv- ;er R is connected with the terminal circuit quency signaling apparatus is shown connected with the terminal circuit by a fourwire arrangement, the invention of Fig. 2 is not so limited inasmuch as the low 'frequency apparatus may be located in a two wire clrcuit, such as L in Figure 1 which, in turn, may be connected with the fourwire circuit by means of a triple winding transformer 'such as is represented by T in Fig. 1. In Figure 2 the transmitter T is side and the output side of the translating circuit by means of transformers T and T, which also are eflicient for low frequency currents. cuit 2 is also connected'with both the input and the output sides of'the translating cir- Thehigh frequency output cir-' cuit by means of the transformers T and T,

which are eflicient for passing high frequency currents. A transformer T efiicient for hi h frequency current-s, connects the high requency input circuit 3' with the translating circuit. A source of highfrequency oscillations G is adapted to impress the high frequency carrier current upon the translating circuit across the winding of a potentiometer. This source of high frequency oscillations is represented as a vacuum tube oscillator, but it is to be understood that any well known form of generator of high frequency sinusoidal oscillations may beused. The high frequency' output and input circuits 2 and 3respectively are con-' nected with the high frequency transmission line L by means of a triple-winding transformer T A high frequency band filter F is connected between the transformer T and the line L in order to permit the passage of oscillations lying within the band of frequencies which this terminal circuit is adapted to transmit and receive. A network N and filter F, are also connected with the transformer T to balance the line L and the filter F respectively.

If in the operation of this circuit' the transmitter T is actuated, low frequency signaling current. will be set up in the input side of the translating circuit, which will modulate the high frequency oscillations from the source'G. impressed across.

the potentiometer 4. The modulated os-. cillations will'be transmitted from the out: put side of the translating circuit by the transformer T to the high frequency out put circuit 2. These oscillations will pass through the filter F, and be impressed upon the branch transmission circuit by the transformer T passing through the filter F and over the line L to the terminal at the opposite end of the latter line. Modulated high frequency oscillations received over the line L will, assuming that they are of the proper frequency to pass through the filter F be impressed upon the high frequency input circuit 3 of the receiving path of the terminal circuit. These oscillations will pass-through the high frequency filter F which is designed to pass one band of frequencies but not the carrier and be impressed by the transformer T upon the transformer T to the low frequency output circuit 1 of the receiving path, and thence to the receiver R,. The function of the transformers T and T inserted .in the input side of the translating circuit, is to balance the translating circuit, so that the carrier oscillations will not be transmitted.

This will be more clearly understood if.

5 consideration be given to what occurs when the unmodulated carrier oscillations are impressed across the potentiometer 4 and no voice c'urrents are im ressed across the windings of the trans ormer T If we 2 consider the condition of the translating circuit at an instant when the point a of t the potentiometer is positive with respect to the point b, the potential of the plate and the negative charge of the grid is diminished, which allows a change in the transfer of energy from the plate to the filament. This flow of current in the output circuit of the translating device, which includes, of course,one of the windings of the transformer T induces a potential in the other winding of the same transformer. Simultaneously the grid current flowing, through thatwinding of transformer T connected with the grid circuit f" will indu e a potential in the line winding of T Owing to the impedance of the windings. of the transformers T T T and, T connected in the grid circuit, the

, magnitude of the grid current is relatively sm all but by proper design out-the 'trans-' formers T and T, the induced otentials in the line windings of T and may be of such magnitude and applied such manner as'to neutralize, in consequence of i which no'iunmodulated carrier current will flow in circuit 2. i

If, -hoWever,lowfrequency signaling currents :arising 'within the low frequency in- --putfj. ci'rcuit are 'ii'n 'ressed, by 'the "transfoi'nier '1 upon the input side of thetrans- -l'ating circuit, the balanced condition of the translating circuit is disturbed thereby' and the modulated high frequency oscillations will be transmitted by the transformer 5 T to the high frequency output circuit 2. These high frequency oscillations will pass through the high frequency band filters-F, and F and betransmitted over the line L or from an antenna. It will be seen" from the foregoing description that this circuit arrangement provides means for the transmission and the [reception of modulated carrier oscillations in which the processes of modulation and demodulation -are performed by a single translating circuit common to the transmitting and receiving paths, the translating circ'uit employing a single tube and being so designed as to substantially suppress the transmission of the unmodulated high frequency oscillations.

Although this invention has been shown as being embodied in certain specific circuit arrangements; it is, of course, to be understood that it is' capable of embodiment in other and different arrangements from those shown, without departing from the spirit of the appended claims. What is claimed is 1. In a signaling system adapted for the transmission and reception of signals of high frequency carrier oscillations the combination withinput circuits and output circuits of a translating circuit having a single translating device and a source of unmodulated high frequency oscillations associated therewith, and a plurality of transformers connecting said input circuits and said output circuits with said translating circuit the said output transformers having their windings so disposed as to balance said translating circuit whereby the transmission there through of unmodulated high frequency oscillations is substantially prevented.

2. In a signaling system, the combination of a translating circuit having associated therewith a translating device, and a source of unmodulated carrier oscillations adapted to be modulated by low frequency currents and to demodulate high frequency modu-' lated currents, high frequency and low fre-v quency input circuits adapted to impress modulated high frequency .and low frequency currents respectively upon said translating circuit, output circuits adapted to receive the resulting low frequency and high frequency currents from the said'trans lating circuit, and a plurality of high frequency and'low frequency transformers connecting said output circuits with the said translating circuit and associated with the input and output sides of the said translatin circuit, whereby the said translating circult is balanced to' substantially prevent the transmission throughthe'said high frequency transformers of unmodulated high frequency oscillations.

3. In a signaling system, the combination of a unilateral translating circuit having associated therewith a source 'of'unmodulated carrier current adapted to be modulated by low frequency currents .and to de modulate high frequency modulated currents, low frequency signaling apparatus connected with the input and outputsides ofsaid translating-circuit, high frequency output and input circuits, means for impressing low frequency currents from said low frequency apparatus and 7 high. fre* quency. currents from said input circuit upon said translating circuit, and trans forming means for impressing the low frequency andhigh' frequency outputcurrents on the respective output circuits, the said latter means having its windings so disposed with respect to the input and output sides of the said translating circuit as to substantiall suppress the transmission of unmodulate high frequency oscillations.

4. The combination with a four-wire terminal circuit adapted for high frequency.

signaling having a translating circuit comm0n..to the transmitting and receiving paths Jfthe said four-wire circuit, low frequency signaling apparatus connected with the input and output sides of the said translating circuit, a-high frequency output and' a high frequency input circuit carrying the hlgh' frequency currents from and to the said translating circuit, and coupling means associated with the output side of the said translating circuit and with the high fre-' quency output circuit, the said coupling means beingso proportioned and connected as to substantially prevent the transmission to the output circuit of unmodulated high frequency current.

5. In a signaling system, the combination;

mon'lto the .said input and output circuits having a thermionic device and asource of high frequency carrier current associated therewith, and means coupling together the -input and output sides of the said'thermionic device and the'said high frequency output circuit the said coupling means being so arranged and proportioned as to substantially neutralize and prevent the transmission to the output circuit of the unmodulated high frequency carrier current.

7. In a signaling system the combination of a, translating circuit characterized by a single thermionic tube and a source of unmodulated high ficqucncy oscillations, a source of low frequency variations, a source 'of high frequency modulated oscillations,

means to impress said low frequency variations and said high frequency modulated oscillations on the translating circuit, and

a. low frequency receiving circuit and a high frequency transmission circuit coupled with the said translating circuit in such a manner current, and low frequenc as to substantially suppress the transmission of .the unmodulated high frequency oscillations.

8. In a signaling system, the combination .of a, translating circuit characterized by a single-thermionic tube having connectedgtherewith a source of unmodulated car-.

rier current, a source of low frequency current for modulating said carrier current and a source of modulated high frequency current to 'be demodulated by the said carrier and high frequency output circuits coup ed with the said translating circuit whereby the resultantmodulated and demodulated currents may be impressed upon their respective high frequency and lowv frequency output circuits, the said coupling being so arranged and proportioned as to substantially prevent the transmission therethrough o'f unmodulated carrier, oscillations.

9. In a. signaling system, the combination with a translating circuit having a thermionic device connected therewith, of a source of carrier frequency current connected therewith, a low frequency input circuit and a low frequency output circuit, each I having means to couple them with the translating circuit, a high frequency input circuit and a high frequency output circuit, each having means to couple them with the translating circuit, the coupling means of the high frequency output circuit being so proportioned and connected as to substantially prevent the transmission therethrough of the unmodulated carrier current, and frequency selecting means connected with the high frequency input circuit designed to pass a frequency or frequencies other than the carrier frequency. I

10. In a, signaling system, the combine tion with a translating circuit having a thermionic device connected therewith, of a source 'of carrier frequenoy current connected therewith, a low frequency input circuit and a. low frequency output circuit, each having means to couple them with the translating circuit, a high frequency input circuit and a high frequency output circuit, each having means to couple them with the translating circuit, the coupling means of the high frequency output circuit being so proportioned and connected as to substantially prevent the transmission therethrough of the unmodulated carrier current, and frequency? selecting means connected with the high frequency input circuit and the high frequency output circuit to pass a frequency or he quencies other than the carrier frequency.

11. In a signaling system, the combination with a vacuum tube translating circuit comprising a plate circuit and a grid circuit, of a source of unmbdulated carrier frequency current connected with the said translating circuit, a high frequency output circuit, means in couple the said output circuit with the said plate and the said grid circuits, the-saidcoupling'means being so proportioned and poled as m substantially prevent the transmission of 'iinmodulated carrier current to the said output circuit meansdo couple the input circuitofnthe said translating circuit, and fre-,

quency selecting means connected with the said inputcircuit to prevenbthe transmis- 10 sion of unmodulated carrier current.

Int'estimony whereof l have signed my name to this specification this 29th day of September 1919.

HERMAN A. AFFEL. 

